1. Field of Invention
The present invention relates to a method of adapting or adjusting so that objects can be caught clearly. More particularly, the present invention relates to a method of auto focusing a photographic apparatus.
2. Description of Related Art
Refer to FIG. 1, FIG. 2 and FIG. 3. Photographic apparatus 100 of digital cameras generally have an auto focus function to help a user to quickly catch an image surface lying within the depth of field. The photographic apparatus 100 includes a lens device 10 with a focusing lens 101, a sensing unit 11, a digital signal processor (DSP) 12, a driving unit 13 and a control unit 15. The driving unit 13 is connected to the sensing unit 11 and the focusing lens 101. The control unit 15 is electrically connected to the digital signal processor 12 and the driving unit 13.
The photographic apparatus 100 uses a method to focus the image surface lying within the depth of field, and the method comprises several steps:
(A) moving the focusing lens 101 to a micro scene position B to complete the initialization task regardless of a start position A (as shown in FIG. 3) when the photographic apparatus 100 is turned on.
(B) then, moving the focusing lens 101 towards a far scene position F at a first speed with the driving unit 13, and simultaneously obtaining multiple continuous optical singles and respectively converting those optical signals into evaluation values;
(C) comparing the evaluation values to acquire a maximum evaluation value by the control unit 15, and stopping the driving unit 13 when an evaluation value 70% of the maximum evaluation value is obtained, wherein the focusing lens temporarily stays at a coarse turning beginning position C.
(D) reversing the driving unit 13 at a second speed that is slower than the first speed to move the focusing lens 101 towards the micro scene position B and simultaneously obtaining the evaluation values until the evaluation values decrease and stop the motion, where the decrease of the evaluation values represents the focusing lens 101 has been moved over the maximum evaluation value and goes back to a previous area, and stays in a fine tuning beginning position D.
(E) reversing the driving unit 13 at a third speed that is slower than the second speed until a maximum evaluation value is substantially obtained again and stopping, where the focusing lens 101 stays in an optimum position E and completes auto focus operations.
Consequently, the aforementioned method helps the user quickly focus the image surface lying in the depth of field regardless of whether the scene being captured is a far scene or a micro scene when the user is trying to find a view. Manual observations with the eyes to manually adjust the focus are unnecessary, which avoids any operational deviations and time.
However, the aforementioned method still has some problems.
First, the traveling behavior of the focusing lens 101 is a shuttle run action as shown in FIG. 2 and FIG. 3. The five movement positions are A, B, C, D and E, and the B, C and D positions are transition positions. The focusing lens 101 needs to be moved in the opposite direction when it reaches the transition positions. Therefore, the driving unit 13 should be temporarily stopped, and then moves the focusing lens 101 towards the opposite direction. The shuttle run movement also wastes time and wears out the components thereby shortening the lifetime of the components and increasing the component failure rate.
Second, the focusing lens 101 moves between two positions E and D as shown in FIG. 3. The total distance moved by the focusing lens 101 is long, which thereby prolongs the focusing time.
Finally, the focusing lens 101 must return to the micro scene position B to perform the initialization operation when the users focus the photographic apparatus 100 each time. If the last picture shot scene that is far away, the start position A is inevitably closer to the far scene position F. However, if the scene currently being shot is still far away, the focusing lens 101 hardly performs the initialization operation with moving a short distance. Instead, the focusing lens 101 must return to the micro scene position B, which causes the focusing lens 101 to travel over a longer distance, consumes time and slow auto focus operations.
Besides, in practical operations, moving the focusing lens 101 exists backlash. The focusing lens 101 needs to move over a longer distance to compensate for the backlash. An increase in shuttling motions of the focusing lens 101 increases the influence of the backlash.
Therefore, there is a need to provide an improved auto focus method to mitigate or obviate the aforementioned problems.